The invention relates to an oscillator-mixer arrangement comprising a dual-gate field effect transistor of the Schottky type, intended to supply an output signal of a frequency which is commonly referred to as an intermediate frequency. The output signal is obtained by subtractively mixing a high frequency input signal and a locally produced signal. The input signal is applied to the first gate electrode (G.sub.1), and the locally produced signal is controlled by the second gate electrode (G.sub.2). The output signal is recovered at the drain (D), while the source (S) is directly connected to ground. The arrangement is used in the field of very high frequency circuits, more specifically the reception of very high frequency waves.
Such a circuit is intended to be incorporated in a front end assembly receiving very high frequency waves, typically having a frequency of 12 GHz, used in the distribution of radio-television programs by means of artificial satellites. These programs can be received by ground-based receiving stations of a comparatively large size, thereafter broadcasted by local networks, or by small community stations serving schools, information centers or houses, and even individuals, particularly in the regions which are not covered by ground-based transmitter networks.
In general, a front end forms the interface between the receiving aerial and the receiver circuits of the television set. It functions to amplify the signal coming from the aerial and to reduce its frequency from 12 GHz to 1 GHz. Front end "assembly" is to be understood to mean that it is formed by integrated circuits, typically by field effect transistors, of gallium arsenide, because of their good very high frequency performance.
Reducing the frequency, from 12 GHz, the frequency assigned by the CCIR to telecommunication by means of artificial satellites, to 1 GHz, the intermediate frequency before demodulation by the circuit of the television receiver, is known from the prior art. It generally requires the presence of a local oscillator having a frequency of approximately 11 GHz, and a mixer from whose output a 1 GHz signal is derived. The respective circuit diagrams of a local oscillator and a mixer, published in Inter Electronique dated Apr. 28, 1978 is mentioned by way of example.
The ever-increasing degree of integration of the receiving front end dictated by the necessity to reduce the manufacturing cost of such a system, has induced applicant to search for a component which combines the functions of mixer and oscillator.
The dual-gate field effect transistor of the Schottky type is suitable for that purpose. From the prior art it is known to use it as a mixer, and the publication entitled: "An X-Band Dual Gate Fet Mixer", by S. C. Cripps et al, Proc. 1977 European Microwave Conference is mentioned as an example. Its use as an oscillator-mixer is also known, and the publication entitled: "A self oscillating dual gate Mesfet X-Band Mixer, with 12 dB conversion gain", by C. Tsironis et al, in the 8th European Microwave Conference Dig. Techn. Papers, Brighton, England, published in September 1979 is mentioned as an example.
In accordance with the last-mentioned publication the second gate electrode of a dual gate MESFET transistor is connected to a line of the variable-length microstrip type, whose end is short-circuited.
This device effectively forms an oscillator-mixer, however, it has the disadvantage that it cannot be stabilized by means of a resonator and for that reason its oscillating frequency is comparatively unstable, which makes impossible its use in the front end for receiving very high frequency waves for television.